Update instructions for extension updates

Author: jakob

http/Resources/conclusion.html

@@ -27,8 +27,12 @@
   <h1>Please restart the PostgreSQL server!</h1>
   <p>pgsql-http @EXTENSION_VERSION@ for PostgreSQL @PG_MAJOR_VERSION@ has been installed successfully.</p>
   <p>
-	  You must stop and restart your PostgreSQL server before using the extension.
-	  After restarting the server, you can enable the extension by running the SQL command <tt>CREATE EXTENSION http;</tt>
+	  If this is a new install, please stop and restart your PostgreSQL server before using the extension.
+	  After restarting the server, you can enable the extension in a database by running the SQL command <tt>CREATE EXTENSION http;</tt>
+  </p>
+  <p>
+	  If you are upgrading from a previous version of the extension, you do not need to restart the server.
+	  Please execute the command <tt>ALTER EXTENSION http UPDATE;</tt> instead. You need to run this command on every database that uses the extension.
   </p>
 
 </body>